When the last Boeing KC-135 Stratotanker is finally retired, sometime in the 21 st cen­tury, the aircraft will have achieved a record as one of the most versatile and long-lived designs in the history of military aviation. Designed primarily as a refueling tanker for the Strategic Air Command, the KC-135 has served as the basis for over forty variants, serving in such roles as transport, electronic reconnaissance, airborne command post, and radio relay, among others. Unlike many of its contemporaries, the KC-135A remains in service and is likely to remain in service for years to come. The same Stratotanker that refueled B-47s and B-52s in the late 1950s may very well be refueling B-2 Stealth bombers and F-23 ATFs during the 1990s.
In-flight refueling can be traced back to June of 1923, when the first airborne transfer of fuel occurred. Two DH-4 biplanes were used: the tanker aircraft trailing a fuel hose/ cable that was physically grabbed by the crew of the receiver aircraft. Using this method, the receiver managed to stay aloft for over thirty-seven hours. This feat soon inspired other record-breaking endurance flights. During January of 1929, the Atlantic-Fokker C-2A, named "Question Mark," made a 150 hour, 11,000 mile flight. During 1935, a Cur-tiss Robin flew a four week longcircuit around an airport in Mississippi. On such flights, engine oil and food also had to be transferred in addition to fuel.